Many signal processing devices and electronic devices, including field programmable gate arrays, require that signals input to the devices be amplified. However, if the signal is over-amplified, the devices may become overpowered, resulting in errors in the processing operation. If the signal is under-amplified, the device may fail to detect the signal or to process the signal properly. Thus, in order to prevent erroneous processing by a signal processing device, the signal to be processed often must be amplified so that the voltage level of the signal is within a particular voltage range.
Unfortunately, the amount of amplification that is required can vary, even for signals produced by the same type of equipment. These variances can be linked to at least two causes. First, pieces of equipment that produce signals often operate in varying environments. Second, the user of the equipment sometimes replaces parts of the equipment with parts that differ from the factory original. As one might expect, such variations in operating conditions and parts often cause variations in the signal produced by the equipment. Thus, in order to maintain the signal within the optimum voltage range, some provisions must be made to ensure that the amount of amplification is adjusted or tuned. In the past, tuning of such equipment was generally complex and inconvenient, as it often required skilled technicians very familiar with the equipment and its operation. These requirements also made maintenance and replacement of the equipment time consuming and expensive.
An example of an application in which it is desirable to maintain a signal within a predetermined range is a linear displacement detector, such as available from Balluff, Inc. and others. A linear displacement detector is a device that measures the linear position of an object. One type of linear displacement detector is a magnetostrictive linear displacement transducer, an example of which is described in European Patent No. 0 149 745 B1 which is assigned to the Assignee of the present application. Typically, a magnetostrictive linear displacement transducer includes a signal generator, a magnetostrictive waveguide, a magnet, a mode convertor, and a displacement determination device. In the transducer, the magnet is disposed linearly along the waveguide. The magnet is connected to an object, so that the position of the magnet corresponds with the position of the object. When an excitation signal is provided near the magnet and waveguide by the signal generator, a mechanical wave, known as a torsion wave, is produced in the waveguide at the position of the magnet. Once the wave is produced, it travels through the waveguide outwardly from the magnet to the mode converter, where it is converted by the mode convertor into an electrical signal. Such a conversion of a mechanical wave into an electrical signal is known as the Wiedemann effect and is typically achieved by using a coil as the mode convertor.
Once the torsion wave is converted into an electrical signal, the signal passes to a displacement determination device. The device determines the distance traveled by the torsion wave, and thus the position of the object, based upon the interval of time between the production of the excitation signal and the production of the signal by the mode convertor. Usually, the device that measures or indicates the time interval is a signal processor or integrated circuit, such as a field programmable gate array, that requires the signal generated by the mode converter to be maintained within a predetermined voltage range in order for proper operation. An amplification stage is often utilized to amplify the signal from the mode convertor so that it falls within the desired range. Unfortunately, because the temperature of the environment in which the transducer operates, as well as the magnet position, affects the amplitude of the signal generated by the mode convertor, even the amplified signal may fall outside of the desired range in certain environments. In addition, different types of magnets may affect the amplitude of the mode convertor signal differently, thus causing the amplified signal to fall outside of the desired range.
Currently, there are a limited number of options available to account for the variables that affect the signal. One such option is to custom-manufacture each transducer to account for the temperature in which the transducer will operate and the type of magnet and waveguide with which it will be used. The customization process includes selecting the proper feedback impedance for the amplification stage and, thus, the proper amplification level. Another option is to tune the unit upon installation to account for the temperature in which the unit will operate, as well as the type of magnet, distance from the waveguide to the magnet, and waveguide to be used. Such tuning can be accomplished by including an impedance selector in the feedback path of the amplification stage and selecting the proper impedance upon installation of the transducer. As mentioned above, these options have proven to be expensive and time-consuming.
Furthermore, prior tuning procedures cannot account for changes to the transducer that may occur after the transducer has been initially installed. For example, if the temperature at the site of operation varies significantly, or if the magnet or waveguide is replaced with parts that differ from the originals, the feedback impedance often must be manually readjusted or replaced in order for the amplified signal to be within the desired range.
Another problem frequently encountered with magnetostrictive linear displacement transducers involves the conductive wire used to transmit the excitation signal produced by the signal generator. Shocks or vibrations within the transducer may cause the conductive wire to contact the waveguide, causing momentary variations of the signal and failure of the transducer. This can be a problem particularly when a solid wire is used for the conductive wire. Such failures can lead to undesirable "crashes" of machinery and equipment, which can create further problems and unreliability.
Accordingly, to overcome the above and other problems, it is desirable to have an apparatus and method for automatically and periodically tuning a signal to within a predetermined voltage range which eliminates the need for manual adjustment or replacement of the amplification stage. Furthermore, it is desirable to have such an apparatus which can be utilized within a linear displacement detector. In addition, it is desirable to have a magnetostrictive linear displacement transducer that is less sensitive to shocks, vibrations, the environment, ambient temperatures and differences between magnets.